Many advances have been made in the production of signage for both indoor and outdoor applications. Printing techniques such as digital ink jet printing allow for the production of high quality color images for a wide range of applications at a low cost. Printable substrates such as fluoropolymer films have been selected that can withstand the effects of dirt, stains, graffiti, sun and other vicissitudes of weather and handling. Moreover, as described in U.S. Pat. No. 6,626,530 to Snow et al., printing with solvent based inks has been employed, eliminating the need for water absorbing layers needed for printing with aqueous based inks. Printing on fluoropolymer films is accomplished in U.S. Pat. No. 6,626,530 by coating the films with a hydrophobic, ink receptive compositions compatible with the fluoropolymer film. The ink receptive compositions enable the printing of images on substrates known for having low surface energy with good release properties.
Solvent-based digital printers utilize low viscosity inks in order to facilitate fluid movement of ink through the print heads. This leads to relatively low concentrations of solid pigment and other additives and, typically, inks are around 10 wt. % solids. Low solids inks necessitate the jetting of high volumes of ink solvent to achieve bright colors. The problem magnifies when multiple ink streams are mixed to achieve a broader color range or more intensely colored regions. Printers commonly use four different inks (cyan, magenta, yellow and black) and more sophisticated printers use as many as eight with a corresponding increase in use of ink solvent per square foot to achieve intensely colored regions.
Ink receptive coatings must be able to accommodate large volumes of ink solvent associated with solvent-based printing to produce intense colors. Use of a single ink jet stream may yield up to 1 ml ink solvent per square foot of ink receptive coating, while the production of an intense solid black image which requires all four ink jet streams in a four color printer will yield up to 4 ml per square foot. If the dry film thickness (dft) of a coating is 25 micrometers, it must absorb roughly 1.7 times its own weight of ink solvent to accommodate the maximum ink output of a four color printer. In many applications thinner ink receptive coatings are desirable, i.e., coatings having a dft of 5 to 10 micrometers are common. A coating of 5 micrometers needs to accommodate more than 8 times its own weight of ink solvent to perform the same function.
There is a need for printable articles having an ink receptive composition for use with non-aqueous solvent based inks that can absorb significantly more ink solvent without adverse effects such as crazing or dissolution.